1. Field of the Invention
The present invention relates to a snowmobile having a steerable ski supported by a front portion of a vehicle body and an endless track device supported by a rear portion of the vehicle body. More particularly, this invention relates to improvements in the rear suspension of a snowmobile.
2. Description of Background Art
A conventional rear suspension for a snowmobile including a rear cushion device consisting of a damper coaxially located within a cushion spring that is provided between the swing arm and the side rail is disclosed in U.S. Pat. No. 4,093,033.
The '033 patent also discloses a conventional endless track device for a snowmobile which includes a drive wheel, a swing arm pivotally supported to a vehicle body, a side rail supported to a rear end of the swing arm and extending in a longitudinal direction of the vehicle body, idlers supported to a front portion and a rear portion of the side rail, and an endless track belt wrapped around the idlers and the drive wheel. In the '033 patent, the side rail is formed with a slider extending in the longitudinal direction for slidably guiding the endless track belt. The front end of the slider extends to a position in the vicinity of the drive wheel.
Further, another conventional endless track device employing a torsion spring for the cushion spring is described in Japanese Patent Laid-open No. Sho 51-14628.
When an impact load is applied from a snow surface to the side rail of the endless track device during operation of the snowmobile, the swing arm is swung upward. This swing of the swing arm due to the impact load must be absorbed by the cushion spring and the damper.
Because the endless track device has a low height, the rear cushion device is conventionally arranged nearly horizontally. As a result, a large damping force must be exerted by the damper to counteract the swing arm movement. For the same reason, the stroke of the damper is reduced. Accordingly, a high-load cushion spring and link mechanism are required in the conventional snowmobile which results in increased weight.
If a torsion spring is used as the cushion spring, a similar weight problem occurs because, in general, torsion springs are heavier than coil springs.
Another problem which occurs in the conventional snowmobile is the instability of the cushion spring due to contact of individual spring elements or deviation of the coil center.